1. Field of the Invention
The present invention relates to a tapping control apparatus for controlling tapping operation of a numerically controlled machine tool, and more particularly to a tapping control apparatus for effecting high-speed, stable tapping operation by automatically determining an acceleration/deceleration constant for the rotational speed of the spindle of a machine tool.
2. Description of the Related Art
Demands for higher-speed machining operation require the tapping operation to be also carried out at higher speed. For tapping metals such as aluminum, it is necessary that the rotational speed of a spindle and the speed of feeding movement along a Z-axis accurately be in synchronism with each other. To meet this requirement, the conventional tapping process employing a floating tapper is replaced with a rigid tapping process which uses a rigid tapper and keeps the rotation of a spindle and the feeding movement along a Z-axis in synchronism through pulse distribution for tapping operation.
The applicant has filed two applications, Japanese Patent Applications Nos. 61-175868 and 61-175869 directed to the rigid tapping process. However, in the tapping disclosed in these applications only one time constant is used for acceleration/deceleration control of the rotation of the spindle and the feeding movement along the Z-axis, with the result that the problem of overshooting or the like is brought about when high-speed tapping operation is performed. If a large time constant is selected, the time required for machining is increased at low-speed operation.